WO1993010160A1 - New thermoplastic fluorocopolymers, and fluoromonomers for use in their manufacture - Google Patents

Abstract

The invention concerns fluoropolymers with enhanced heat stability and improved resistance to deformation when hot. The fluoropolymers are made from fluoroethylenes, using as comonomers perfluoro cylcoalkyl vinyl ethers and, optionally, other comonomers. The invention also concerns the perfluoro cycloalkyl vinyl ethers which give the fluoropolymers described their useful thermal properties.

Description

New thermoplastic fluoropolymers and fluoromonomers for use in their manufacture

The present invention relates to fluoropolymers with improved temperature resistance and heat resistance on the basis of fluoroethylenes, perfluoro (cycloalkyl vinyl ether) and optionally further comonomers being used as comonomers. The present invention also relates to the perfluoro (cycloalkyl vinyl ethers) which impart the advantageous thermal properties to the fluoropolymers according to the invention.

Fluoropolymers are used in engineering whenever special properties, such as low surface tension, high resistance to chemicals, oils and solvents, or extreme demands on the

(Heat) aging stability are required.

As the largest bulk plastic in the field of fluoropolymers, polytetrafluoroethylene (PTFE) combines these properties in an excellent way. However As is known, PTFE cannot be processed thermoplastically. The thermoplastic processability can be improved by introducing comonomers. which lower the viscosity of the polymer above the softening point (melting point in partially crystalline systems), and thus improve the melt flow. Examples of such comonomers are hexafluoropropene and perfluorinated acyclic alkyl vinyl ethers (US Pat. No. 3,180,895). In most cases, however, the introduction of such comonomers r lowers the softening point of the copolymer itself, so that the thermoplastic processability is at the expense of the temperature stability of the polymer.

Other fluorine-containing homopolymers such as polyvinylidene fluoride or polychlorotrifluoroethylene can be processed thermoplastically, but because of their low fluorine content they achieve the Properties often do not match the level of highly fluorinated

 (Co) polymers is achieved. The object of the present invention is to provide new thermoplastically processable fluoropolymers with increased temperature and heat resistance based on fluorine-containing ethylenes as the one comonomer.

It has been found that it is possible to copolymerize fluorine-containing ethylenes with perfluoro (cycloalkyl vinyl ethers) of the following formula I, thermoplastic copolymers with increased temperature and

n = 0,1 oder 2 To produce heat resistance.

n = 0.1 or 2

m = 3, 4 or 5.

To modify the properties of the fluoropolymers according to the invention, further comonomers can be used

Copolymerization can be used. These include in particular straight-chain or branched C ₃ to C ₈ alkenes with at least one fluorine atom or fluorine-free ethylene or propylene.

The present invention accordingly relates to thermoplastic fluoropolymers which have been obtained by copolymerizing a) 99.5 to 50 mol% of at least one ethylene having 1 to 4 fluorine atoms, and b) 0.5 to 50 mol% of at least one perfluoro ( cycloalkyl vinyl ether) of the formula I and c) 0-40 mol% of at least one further comonomer from the group consisting of ethylene, propylene and at least one fluorine-containing straight-chain or branched C ₃ -C ₈ -alkenes. The molar ratio of fluoroethylenes to perfluoro (cycloalkyl vinyl ethers) in the fluoropolymer according to the invention is preferably between 1 and 50, particularly preferably between 2 and 20. Tetrafluoroethylene, trifluoroethylene, vinylidene fluoride, monofluoroethylene are used as ethylenes (component a)) containing at least 1 fluorine atom or chlorotrifluoroethylene in question. Tetrafluoroethylene or vinylidene fluoride are preferably used.

Of the perfluoro (cycloalkyl vinyl ethers) according to formula I, those with n = 0 are preferred. Perfluoro (cyclopentyl vinyl ether) is particularly preferred according to the invention, that is to say according to formula I n = 0 and m = 4.

The perfluoro (vinyl-cycloalkyl) ethers according to the invention are produced from 2-cycloalkoxypropanecarboxylic acid fluoride (obtainable according to US Pat. No. 3,274,239). In principle, they are obtainable by conversion into their alkali metal salts and subsequent decarboxylation at 170 to 250 ° C., as described in US Pat. No. 3,274,239. However, considerable amounts of 1,1,1,2-tetrafluoroethylcycloalkyl ethers are formed as a by-product, which can be removed only with difficulty and with the loss of high yields. Residues of such by-products significantly impair the copolymerization and lead to fluoropolymers with inadequate mechanical and thermal properties. The difficulties mentioned to produce perfluoro (cycloalkyl vinyl ether) in a form suitable for copolymerization with fluoroethylenes are to be regarded as the reason why they have not previously been used in fluoropolymers. It has now been found that it is possible to convert 2-cycloalkoxypropanecarboxylic acid fluoride in a form suitable for the preparation of fluoropolymers into perfluoro (-vinylcycloalkyl) ether if a process analogous to the process disclosed in EP-A 260 773 is used.

According to the invention, the perfluoro (cycloalkyl vinyl ethers) of the formula I to be used in the copolymerization are prepared from the corresponding 2-cycloalkoxypropanecarboxylic acid fluorides in accordance with the following formula II

in dem diese in einem geeigneten Lösungsmittel, das ein salzbildendes Mittel enthält, in Gegenwart einer katalytischen Menge von N,N-Dimethylformamid langsam bis zu einer Temperatur von 110 - 140°C erhitzt wird, bei einer Temperatur ab 100 - 120°C ein Destillat entsprechend einer Kondensationstemperatur zwischen 60 und 90°C abgezogen wird, und das Destillat bei Normaldruck redestilliert wird.

in which it is slowly heated to a temperature of 110-140 ° C in a suitable solvent containing a salt-forming agent in the presence of a catalytic amount of N, N-dimethylformamide, at a temperature of 100-120 ° C a distillate is drawn off according to a condensation temperature between 60 and 90 ° C, and the distillate is redistilled at normal pressure.

Diglyme (diethylene glycol dimethyl ether) is preferably used as the solvent. Anhydrous potassium carbonate is preferred as the salt-forming agent

used. The salt-forming agent is preferred as used in a 1.1 - 1.3 molar excess based on perfluoro-2-cycloalkoxy-propanecarboxylic acid fluoride. Dimethylformamide is preferably used in amounts of 1-5% by weight, based on the solvent. An absolutely water-free working method is essential.

The free radical processes known for the copolymerization of fluorine-containing monomers can be used to prepare the copolymers according to the invention; it can be copolymerized in solution, suspension or emulsion (US 2,968,649; US 3,051,677J

US 3,053,818; US 3,331,823; US 3,335,106 with an example of the possible reaction media and general reaction conditions). In principle, known compounds which are suitable for the respective reaction medium are used to initiate the radical copolymerization. For example, organic, oil-soluble peroxides, which can also be fluorinated, such as benzoyl peroxide, trifluoroacetyl peroxide or organic soluble azo compounds, such as azobisisobutyronitrile, are used in solution and suspension polymerization. In emulsion polymerization, which is preferred for the preparation of the copolymers according to the invention, water-soluble inorganic per compounds are used as initiators, such as persulfates, perborates, percarbonates etc., generally in the form of their sodium or ammonium salts.

Depending on the polymerization temperature and the decomposition constant of the initiator, when using lower temperatures for polymerization

Decay accelerators, usually reducing agents, can also be used. Can serve as such; Sulfur compounds such as sodium sulfite, sodium pyrosulfite or Rongalit C (sodium formamidine sulfinic acid), furthermore organic reducing agents such as ascorbic acid, metal salts such as iron (II) or cobalt (IΙ) salts, organometallic compounds etc.

The reaction temperatures for the copolymer are between -15 and + 120 ° C, preferably 20 to 90 ° C.

To adjust the molecular weight of the resulting polymers, chain transfer agents such as methanol, isopropanol, isopentane, ethyl acetate, diethyl malonate and carbon tetrachloride can be used if necessary.

It is a further characteristic of the process according to the invention that the copolymerization is carried out under increased pressure. This pressure should be at least 5 bar, but need not exceed 100 bar.

A preferred range for the process according to the invention is 5 to 65 bar.

The copolymers according to the invention can be prepared in batches, but preferably by semi-continuous or continuous processes. Linear copolymers with molecular weights of 10 ³ to 10 ⁶ g / mol are obtained.

The invention is illustrated by the following examples:

Example 1 a) Preparation of Perfluoro-2-cyclopentoxypropanecarboxylic Acid Fluoride 150 g (2.59 mol) of calcined potassium fluoride are suspended in 500 ml of diglyme and 456 g (2.0 mol ) Octafluorocyclopentanone condensed. After the slightly exothermic reaction has subsided, the mixture is cooled again to about 5 ° C. and hexafluoropropene oxide is introduced so rapidly that only weak reflux occurs on the dry ice cooler. After 330 g (1.99 mol) of hexafluoropropene oxide have been introduced (about 60 g / h), the mixture is stirred at 5 ° C. for 1 h and at room temperature overnight.

The product is then distilled off under reduced pressure (up to 20 mbar) (bp. Up to 60 ° C.), and a two-phase distillate is collected in the cooled receiver. The upper phase consists of approx. 90% diglyme, the lower phase (approx. 80%)

Product) can be used in the next step without further cleaning.

For characterization and determination of the yield, the crude product (lower phase) is redistilled at normal pressure over a short column. Conversion to perfluorocyclopentyl vinyl ether

175 g (1.26 mol) of powdered anhydrous potassium carbonate and 3 ml of dimethylformamide are placed in 200 ml of absolute diglyme, and 394 g (1.0 mol) of perfluoro-2-cyclopentoxypropanecarboxylic acid fluoride are added dropwise at room temperature in 1 h. Slightly exothermic (up to approx. 35 ° C), after the addition is complete, the mixture is slowly heated to 60 ° C, 80 ° C and 110 ° C (each approx. 1 h, from 80 ° C slight reflux and CO ₂ elimination, from 110 ° C, a distillate can be withdrawn via a bridge). The bottom temperature is increased to max. 130 ° C increased, the top temperature of the distillate fluctuates between 65 - 85 ° C. The crude product (280 g) is redistilled over a 40 cm column at normal pressure:

Main fraction Kp ₁₀₁₃ : 80 - 82 ° C

Yield: 255 g (78 yd. Th.)

(GC-) MS: m / _e = 328 (Molpeak)

¹⁹ F-NMR: δ = -35, ° ppm (2d, 1F, ^J FF = 83 and 65 Hz,

 CF = C-O cis);

-42.1 ppm (4m, 1F, ^J FF = 111, 83 u.

6 Hz, CF = C-O trans);

-51.1 ppm (pseudo-quartet (AA'BB 'higher order system), 4F, "J" = 258 Hz, 2CF ₂ );

 -52.5 ppm (pseudo-quartet (AA'BB 'system of higher order), 4F, "J" =

258 Hz, 2CF ₂ );

-56.5 ppm (4m, 1F, J _FF = 111.65 and 6 Hz, = CFO) and

 -58.8 ppm (m, 1F, OCF) (vs. ext.

CF ₃ COOH). According to GC, the 1,1,1,2-tetrafluoroethylperfluorocyclopentyl vinyl ether content is <2%.

The perfluoro (cyclopentyl vinyl ether) prepared according to this example was used in the polymerization examples 3, 4, 5 and 6.

Comparative Example 1b

Transfer analogous to the process of US Pat. No. 3,274,239

394 g (1.0 mol) of perfluoro-2-cyclopentoxypropanecarboxylic acid fluoride are dissolved in 300 ml of dioxane and made alkaline with phenolphthalein using 40.5 g of sodium hydroxide in 100 ml of H ₂ O. The solvent is then removed in a water jet vacuum and the remaining salt is dried. The dry salt is then thermally decomposed (170-250 ° C) in an oil pump vacuum (0.3 mbar) and the reaction gases are condensed in a trap cooled to -78 ° C.

This crude product (295 g) has a GC purity of 55% (45%. 1,1,1,2-tetrafluoroethyltrifluorovinylether) and cannot be enriched by distillation above 90%.

A polymerization experiment with the crude product or with the enriched product led to discolored products with very low yields, as comparative example 6 shows. Example 2

Manufacture of perfluorocyclobutyl vinyl ether

Analogously to Example 1b), 69 g (0.2 mol) of perfluoro-2-cyclobutoxypropanecarboxylic acid fluoride (prepared from

Perfluorocyclobutanone and hexafluoropropene oxide analogously to Example 1a), the perfluorocyclobutanone (which was obtained according to J. Chem. Soc. 7370 (1965) from 1-methoxy-pentafluorocyclobut-1-ene and elemental fluorine and subsequent hydrolysis of the methylcyclobutyl ether) being reacted with K ₂ CO ₃ becomes.

Yield: 41 g of perfluorobutyl vinyl ether = 74% of theory. Th.

Kp _ND : 59 - 60 ° C

Lt. GC / MS content of 1,1,1,2-tetrafluoroethyl perfluorocyclobutyl ether <3%.

Example 3

Preparation of a vinylidene fluoride / perfluoro (cyclopentyl vinyl ether) copolymer 250 ml of deionized water were placed in a 0.7 l autoclave. 3.9 g of sodium perfluorooctanoate and 3.0 g of potassium peroxydisulfate were dissolved therein. This solution was adjusted to a pH of about 10 with sodium hydroxide. Then the closed autoclave was pressurized three times with a nitrogen pressure of 10 bar and then depressurized to normal pressure. 36 g of perfluoro (cyclopentyl vinyl ether) and 64 vinylidene fluoride were added to the autoclave and the reaction mixture was heated to 50 ° C. with stirring. After a reaction time of one hour at this temperature, 50 ml of an aqueous solution containing 1 g of ascorbic acid, 5 mg of iron (II) sulfate and 1.5 g of sodium hydroxide were uniformly pumped in within 10 h. After this time, in which the reaction pressure decreased from 42 bar to 13 bar, the contents of the autoclave were cooled and the unreacted gas mixture was vented off. The reaction mixture thus obtained was poured into 300 ml of a 4% aqueous magnesium sulfate solution for complete coagulation. The product was washed with water and then dried to give 81 g of a white powder which was identified as a copolymer consisting of units of vinylidene fluoride and perfluoro (cyclopentyl vinyl ether). The copolymer is soluble in dimethylformamide and dimethylacetamide. The

Intrinsic viscosity is 0.2 dl / g (DMF, 25 ° C). The molar ratio of vinylidene fluoride to perfluoro (cyclopentyl vinyl ether) in the copolymer was determined by ¹⁹ F nuclear magnetic resonance spectroscopy and is 91: 9.

The following chemical shifts were found and evaluated in dimethylformamide-d ₇ against the standard trifluoroacetic acid:

a : - 14 ; - 16 ; -17; -46 ppm

a: - 14; - 16; -17; -46 ppm

 b: -42 ppm

 c: -43 ppm

 d: -52 ppm

 e, e ': - 30; -35; -53; -59 ppm

 f, f: -32; -38; -49; -55 ppm

Comparative Example 3 Preparation of a vinylidene fluoride / perfluoro (n-propyl vinyl ether) copolymer

32 g of perfluoro (n-propyl vinyl ether) and 68 g of vinylidene fluoride were copolymerized analogously to the procedure described in Example 3. 72 g of one

Copolymers consisting of units of vinylidene fluoride and perfluoro (n-propyl vinyl ether) isolated. The copolymer is soluble in dimethylformamide and dimethylacetamide. The intrinsic viscosity is 0.81 dl / g (DMF, 25 ° C). The chemical composition was determined by F nuclear magnetic resonance spectroscopy. The molar ratio of vinylidene fluoride to perfluoro (n-propyl vinyl ether) is 91: 9.

Example 4

110 ml of deionized water were placed in a 0.3 l autoclave. 1.8 g of sodium perfluorooctanoate were dissolved therein. This solution was made with sodium hydroxide adjusted to a pH of about 10. Then the closed autoclave was then depressurized three times to normal pressure. 9 g of perfluoro (cyclopentyl vinyl ether) and 21 g of vinylidene fluoride were added to the autoclave and the reaction mixture was heated to 80 ° C. with stirring. After reaching this temperature, 20 g of an aqueous solution containing 0.7 g of ammonium peroxide sulfate were pressed into the autoclave. After a total reaction time of 7 hours, during which the reaction pressure decreased from 38 to 15 bar, the contents of the autoclave were cooled and the unreacted gas mixture was vented off. The emulsion thus obtained was poured into 130 ml of a 4% aqueous magnesium sulfate solution to completely coagulate. The product was washed with water and then dried to obtain 19 g of a copolymer (white powder) consisting of units of vinylidene fluoride and perfluoro (cyclopentyl vinyl ether). The copolymer is soluble in dimethylformamide and dimethylacetamide. The intrinsic viscosity is 0.2 dl / g (DMF, 25 ° C). The chemical composition was determined by ¹⁹ F nuclear magnetic resonance spectroscopy. The molar ratio of vinylidene fluoride to perfluoro (cyclopentyl vinyl ether) is

93: 7. Comparative Example 4

Analogous to the procedure described in Example 4, 9.5 g of perfluoro (n-propyl vinyl ether) and 20.5 g of vinylidene fluoride were copolymerized. 19 g of a copolymer consisting of units of vinylidene fluoride and perfluoro (n-propyl vinyl ether) was isolated. The Copolymer is soluble in dimethylformamide and dimethylacetamide. The intrinsic viscosity is 0.7 dl / g (DMF, 25 ° C). The chemical composition was also determined by ¹⁹ F nuclear magnetic resonance spectroscopy. The molar ratio of vinylidene fluoride to perfluoro (n-propyl vinyl ether) is 92: 8.

On the according to the above examples

 Copolymers prepared were DSC and

 thermogravimetric (TGA) analyzes carried out,

Measurements: TGA measuring device TGS-2 (Perkin-Elmer);

 Heating at 20 K / min under nitrogen from room temperature to complete decomposition.

 DSC - DSC-2 measuring device (Perkin-Elmer);

 twice heating at 20 K / min under helium from -50 ° C to + 200 ° C (measured values from 2nd heating).

Be i sp i e l 5

Example 5

130 ml of deionized water were placed in a 0.3 l autoclave. 0.5 g of lithium perfluorooctane sulfonate was dissolved therein. This solution was adjusted to a pH of about 10 with lithium hydroxide. Then the closed autoclave was pressurized three times with a nitrogen pressure of 10 bar and then depressurized to normal pressure. 9.3 g of perfluoro (cyclopentyl vinyl ether) and 30 g of chlorotrifluoroethylene were added to the autoclave and the reaction mixture was heated to 90 ° C. with stirring. After reaching this temperature, 20 g of an aqueous solution containing 0.8 g of potassium peroxide sulfate were pressed into the autoclave. After a total reaction time of 1.5 h, in which the reaction pressure decreased from 19 to 15.5 bar, the

Autoclave content cooled and the unreacted gas mixture vented. The reaction mixture thus obtained was poured into 130 ml of a 4% aqueous magnesium sulfate solution for complete coagulation. The product was washed with water and then dried to obtain 7.5 g of a copolymer consisting of units of chlorotrifluoroethylene and perfluoro (cyclopentyl vinyl ether). The copolymer is not soluble in dimethylformamide and dimethylacetamide.

The following copolymer composition was determined on the basis of the analyzes of the chlorine and fluorine content:

Chlorotrifluoroethylene / perfluoro (cyclopentyl vinyl ether) = 95/5 (molar ratio). Example 6

Analogously to the procedure described in Example 5, 8.9 g of perfluoro (cyclopentyl vinyl ether) and 60 g of chlorotrifluoroethylene were copolymerized at 70 ° C. for 2 hours. 26 g of a white powder were isolated, which was identified as a copolymer consisting of units of chlorotrifluoroethylene and perfluoro (cyclopentyl vinyl ether). The following copolymer composition was determined on the basis of the analyzes of the chlorine and fluorine content:

 Chlorotrifluoroethylene / perfluoro (cyclopentyl vinyl ether) = 98/2 (molar ratio) Comparative example to Example 6

Analogously to the procedure described in Example 6, 15 g of the perfluoro (cyclopentyl vinyl ether) prepared according to Comparative Example 1b, which could only be provided in 55% purity according to this process variant, and 60 g of chlorotrifluoroethylene were copolymerized at 70 ° C. for 6 h. In addition to 0.2 g of a beige-colored coagulate, 11 g of an ocher-colored powder were isolated from the emulsion which, in addition to units of chlorotrifluoroethylene and perfluoro (cyclopentyl vinyl ether) bound in the copolymer, contains large amounts of unidentified impurities. Example 6 Comparative Example 6

Yield 43% in 2 h 22% in 6 h

Appearance white powder ocher powder + beige coagulate

Claims

Claims 1. Thermoplastic fluorocopolymers obtained by copolymerization of a) 99.5 to 50 mol% of at least one ethylene with 1 to 4 fluorine atoms, and b) 0.5 to 50 mol% of at least one perfluoro (cycloalkyl vinyl ether) of the formula I and

n = 0.1 or 2 m = 3, 4 or 5 c) 0 to 40 mol% of at least one further comonomer from the group consisting of ethylene, propylene and straight-chain or branched C _{3 to} C 8 alkenes containing at least one fluorine atom. 2. Perfluoro (cycloalkyl vinyl ether) of the formula

n = 0.1 or 2  m = 3, 4, 5 or 6, prepared from the corresponding 2-cycloalkoxypropanecarboxylic acid fluorides according to formula II below

in which it is slowly heated up to a temperature of 110-140 ° C in a suitable solvent containing a salt-forming agent in the presence of a catalytic amount of N, N-dimethylformamide, at a temperature of 100-120 ° C Distillate is drawn off according to a condensation temperature between 60 and 90 ° C, and the distillate is redistilled at normal pressure. 3. Perfluoro (cycloalkyl vinyl ether according to claim 2, characterized by a content of 1,1,1,2-tetrafluoroethyl cycloalkyl ethers of less than 4% by weight. 4 4. A process for the preparation of thermoplastic fluoropolymers according to claim 1, characterized in that the perfluoro-cycloalkylvinylether) of the formula I is prepared from the corresponding 2-cycloalkoxypropanecarboxylic acid fluorides according to the following formula II

by slowly heating it to a temperature of 110-140 ° C in a suitable solvent containing a salt-forming agent in the presence of a catalytic amount of N, N-dimethylformamide, at a temperature of 100-120 ° C Distillate is drawn off according to a condensation temperature between 60 and 90 ° C, and the distillate is redistilled at normal pressure.